1. Field of the Invention
The present invention relates to an implant-type chemical supply device that is implanted in a body, for gradually supplying chemicals to the affected part.
2. Description of the Related Art
An implant-type chemical supply device that supplies chemicals to the affected part is generally made up of a chemical tank, a pump unit, a drive control circuit for the pump unit, and a battery for operation of the device, and supplies the chemicals within the chemical tanks to the affected part through a tube.
The pump unit is structured in such a manner that a part of the tube connected to the chemical tank is U-shaped, and rollers on both ends of an actuating lever are in contact with the tube at a predetermined pressure. The actuating lever is rotationally driven by a step motor to extrude chemicals within the tube in the same direction, and the chemicals are supplied to the affected part by this pressure.
The step motor is driven in such a manner that a dividing signal obtained by sequentially dividing an oscillation signal from an oscillating circuit by a frequency dividing circuit is converted by a pulse synthesizing circuit into two signals which are, for example, 10 msec in pulse width, 62.5 msec in period and 31.25 msec in phase difference, whereby inversion pulses of a current whose flowing direction is changed every 31.25 msec are supplied to a coil of the step motor, and a rotor magnetized to two polarities is sequentially rotated every 180 degrees.
By the way, a drive pulse width (10 msec in the above example), a coil resistance, the number of winding of the coil, the dimensions of the respective portions of the step motor, etc., are designed in such a manner that the step motor can be driven stably even in any predicted circumstances with which the device may encounter. The predicted circumstances include a case in which at least only one roller is pressed for rotating while the roller is pressed against the tube, and a case in which at least two rollers are pressed against the tube. The rollers are redesigned as to rotate while the maximum number of rollers is pressed against the tube. Further, because the step motor is so designed as to be driven stably even if the circumstances such as the hardness of the tube, the viscosity of chemicals or the like are different, a drive pulse having an effective power of a certain level or more is supplied to the coil of the step motor even when a large output torque is not required.
Therefore, in the case where the step motor is low in load, a useless energy is supplied to the step motor from the battery, resulting in reduction of the lifetime of the battery.